Dual mixed refrigerant system

ABSTRACT

Processes and systems are provided for recovering a liquefied natural gas (LNG) stream from a hydrocarbon-containing feed gas stream using dual closed-loop mixed refrigerant cycles. In particular, the processes and systems described herein can be used to efficiently and effectively liquefy methane from a hydrocarbon-containing feed gas stream by utilizing a first refrigeration system and a second refrigeration system in fluid communication with a turboexpander and separator.

BACKGROUND

1. Field of the Invention

The present invention is generally related to processes and systems for recovering a liquefied natural gas (“LNG”) from a hydrocarbon-containing gas. More particularly, the present invention is generally related to processes and systems that comprise a dual mixed refrigerant system.

2. Description of the Related Art

In recent years, the demand for natural gas has increased. In many instances, natural gas is found in areas that are remotely located from the markets for the natural gas. Unless the natural gas is located sufficiently close to a market place so that it is feasible to construct a pipeline to transport the natural gas, it must be transported by tankers or the like. The transportation of natural gas as a vapor requires prohibitively large tanker volumes; therefore, the natural gas is customarily liquefied for storage and transportation. The use of liquefied natural gas and methods for its storage are well known. Natural gas may also be liquefied at the point of use when it is available in surplus but may be needed in larger volumes than can be delivered to the point of use in the future. Such storage may be used, for instance, to meet a wintertime peak demand for natural gas in excess of that available through an existing pipeline system during the winter peak demand periods. Various other industrial applications require that natural gas be liquefied for storage.

Previously, substances such as natural gas have been liquefied by processes such as those shown in U.S. Pat. No. 4,033,735, which utilize a single mixed refrigerant. Such processes have many advantages over other processes such as cascade systems, in that they require less expensive equipment and are less difficult to control. Unfortunately, the single mixed refrigerant processes require somewhat more power than the cascade systems.

Cascade systems, such as the system shown in U.S. Pat. No. 3,855,810, basically utilize a plurality of refrigeration zones in which refrigerants of decreasing boiling points are vaporized to provide cooling. However, cascade systems still suffer from operating inefficiencies.

Despite the advances made in natural gas liquefaction technologies, improvements are still needed in regard to operating efficiencies and power consumption.

SUMMARY

One or more embodiments described herein concern a process for liquefying a hydrocarbon-containing gas. The process comprises: (a) introducing a first mixed refrigerant and a feed stream comprising the hydrocarbon-containing gas into a first refrigeration system; (b) cooling at least a portion of the feed stream in the first refrigeration system via indirect heat exchange with the first mixed refrigerant to form a first cooled feed stream; (c) cooling at least a portion of the first cooled feed stream in a second refrigeration system via indirect heat exchange with a second mixed refrigerant to form a second cooled feed stream; (d) expanding at least a portion of the first cooled feed stream or the second cooled feed stream in a turboexpander to form an expanded feed stream; (e) separating at least a portion of the expanded feed stream in a separator to form an overhead vapor fraction and a liquid bottom fraction; (f) cooling at least a portion of the overhead vapor fraction in the first refrigeration system or the second refrigeration system; and (g) driving a compressor with the turboexpander.

One or more embodiments described herein concern a process for liquefying a hydrocarbon-containing gas. The process comprises: (a) introducing a first mixed refrigerant and a feed stream comprising the hydrocarbon-containing gas into a first refrigeration system; (b) cooling at least a portion of the feed stream in the first refrigeration system via indirect heat exchange with the first mixed refrigerant to form a first cooled feed stream; (c) cooling at least a portion of the first cooled feed stream in a second refrigeration system via indirect heat exchange with a second mixed refrigerant to form a second cooled feed stream; (d) separating at least a portion of the second cooled feed stream in a separator to form an overhead vapor fraction and a liquid bottom fraction; and (e) cooling at least a portion of the overhead vapor fraction in the first refrigeration system or the second refrigeration system.

One or more embodiments described herein concern a system for liquefying a hydrocarbon-containing gas. The system comprises: (a) a first refrigeration system comprising a first cooling zone disposed therein, wherein the first cooling zone is configured to cool a feed stream comprising the hydrocarbon-containing gas via indirect heat exchange with a first mixed refrigerant to form a first cooled feed stream; (b) a first closed-loop mixed refrigeration cycle at least partially disposed within the first refrigeration system, wherein the first closed-loop mixed refrigeration cycle comprises the first mixed refrigerant; (c) a second refrigeration system in fluid communication with the first refrigeration system, wherein the second refrigeration system comprises a second cooling zone disposed therein, wherein the second cooling zone is configured to cool the first cooled feed stream via indirect heat exchange with a second mixed refrigerant to form a second cooled feed stream; (d) a second closed-loop mixed refrigeration cycle at least partially disposed within the second refrigeration system, wherein the second closed-loop mixed refrigeration cycle comprises the second mixed refrigerant; (e) a turboexpander in fluid communication with the first refrigeration system or second refrigeration system, wherein the turboexpander is configured to expand the first cooled feed stream or the second cooled feed stream into an expanded stream; (f) a separator in fluid communication with the turboexpander, wherein the separator is configured to separate the expanded stream into an overhead vapor fraction and a liquid bottom fraction; (g) a conduit for returning at least a portion of the overhead vapor fraction to the first refrigeration system or second refrigeration system; and (h) a compressor at least partially driven from work derived from the turboexpander, wherein the compressor is configured to at least partially compress the first mixed refrigerant, the second mixed refrigerant, or the overhead vapor fraction.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments of the present invention are described herein with reference to the following drawing figures, wherein:

FIG. 1 depicts a dual closed-loop mixed refrigerant system for recovering a liquefied natural gas stream from a feed gas stream according to one embodiment of the present invention;

FIG. 2 depicts a dual closed-loop mixed refrigerant system comprising a turboexpander, heavies separator, and compressor connected to the first refrigeration system according to one embodiment of the present invention;

FIG. 3 depicts a dual closed-loop mixed refrigerant system comprising a turboexpander and heavies separator connected to the first refrigeration system and a compressor connected to the first closed-loop mixed refrigeration cycle according to one embodiment of the present invention;

FIG. 4 depicts a dual closed-loop mixed refrigerant system comprising a turboexpander and heavies separator connected to the first refrigeration system and a compressor connected to the second closed-loop mixed refrigeration cycle according to one embodiment of the present invention;

FIG. 5 depicts a dual closed-loop mixed refrigerant system comprising a turboexpander, heavies separator, and compressor connected to the second refrigeration system according to one embodiment of the present invention;

FIG. 6 depicts a dual closed-loop mixed refrigerant system comprising a turboexpander and heavies separator connected to the second refrigeration system and a compressor connected to the first closed-loop mixed refrigeration cycle according to one embodiment of the present invention; and

FIG. 7 depicts a dual closed-loop mixed refrigerant system comprising a turboexpander and heavies separator connected to the second refrigeration system and a compressor connected to the second closed-loop mixed refrigeration cycle according to one embodiment of the present invention.

DETAILED DESCRIPTION

The following detailed description of embodiments of the invention references the accompanying drawings. The embodiments are intended to describe various aspects of the invention in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments can be utilized and changes can be made without departing from the scope of the claims. The following detailed description is, therefore, not to be taken in a limiting sense. The scope of the present invention is defined only by the appended claims, along with the full scope of equivalents to which such claims are entitled.

The present invention is generally related to processes and systems for liquefying a hydrocarbon-containing gas to thereby form an LNG stream comprising methane. As described below, these processes and systems can utilize a dual mixed refrigerant system to assist in the liquefaction of methane from the hydrocarbon-containing gases. Various embodiments of the dual mixed refrigeration system are described further below in accordance with FIGS. 1-7.

Turning now to FIG. 1, a schematic depiction of an LNG recovery facility 10 configured according to one or more embodiments of the present invention is provided. The LNG recovery facility 10 can be operable to condense and subcool a substantial portion of the methane in the incoming hydrocarbon-containing gas feed stream by cooling the gas with a first refrigeration system 12 and a second refrigeration system 14. Additional details regarding the configuration and operation of LNG recovery facility 10, according to various embodiments of the present invention, are described below in reference to FIGS. 1-7.

As shown in FIG. 1, a hydrocarbon-containing gas feed stream can initially be introduced into the LNG facility 10 via conduit 110. The hydrocarbon-containing gas can be any suitable hydrocarbon-containing fluid stream, such as, for example, a natural gas stream, a syngas stream, a cracked gas stream, associated gas from oil production, or combinations thereof. The hydrocarbon-containing gas stream in conduit 110 can originate from a variety of gas sources (not shown), including, but not limited to, a natural gas pipeline distribution network; a hydrocarbon production well; an unconventional gas production unit; a petrochemical processing unit; a coal bed processing unit; a refinery processing unit, such as a fluidized catalytic cracker (FCC) or petroleum coker; or a heavy oil processing unit, such as an oil sands upgrader.

Depending on its source, the hydrocarbon-containing gas can comprise varying amounts of methane, nitrogen, hydrogen, carbon monoxide, carbon dioxide, sulfur-containing species, and other hydrocarbons. For example, the hydrocarbon-containing gas can comprise at least 1, 5, 10, 15, or 25 and/or not more than 99, 95, 90, 80, 70, or 60 mole percent of methane. More particularly, the hydrocarbon-containing gas can comprise in the range of 1 to 99, 5 to 95, 10 to 90, 15 to 80, or 25 to 70 mole percent of methane. It should be noted that all mole percentages are based on the total moles of the hydrocarbon-containing gas.

In various embodiments, the hydrocarbon-containing gas comprises little to no hydrogen. For example, the hydrocarbon-containing gas can comprise less than 10, 5, 1, or 0.5 mole percent of hydrogen.

In various embodiments, the hydrocarbon-containing gas can comprise little to no carbon monoxide. For example, the hydrocarbon-containing gas can comprise not more than 20, 10, 5, or 1 mole percent of carbon monoxide.

In various embodiments, the hydrocarbon-containing gas can comprise little to no nitrogen. For example, the hydrocarbon-containing gas can comprise not more than 20, 10, 5, or 1 mole percent of nitrogen.

In various embodiments, the hydrocarbon-containing gas can comprise little to no carbon dioxide. For example, the hydrocarbon-containing gas can comprise not more than 20, 10, 5, or 1 mole percent of carbon dioxide.

In various embodiments, the hydrocarbon-containing gas can comprise little to no sulfur-containing compounds, which includes any compounds containing sulfur. For example, the hydrocarbon-containing gas can comprise not more than 20, 10, 5, or 1 mole percent of sulfur-containing compounds.

Furthermore, the hydrocarbon-containing gas can comprise some amount of C₂-C₅ components, which includes paraffinic and olefinic isomers thereof. For example, the hydrocarbon-containing gas can comprise less than 30, 25, 15, 10, 5, or 2 mole percent of C₂-C₅ components.

Additionally, the hydrocarbon-containing gas can comprise some amount of C₆₊ components, which includes hydrocarbon-based compounds having a carbon chain length of at least 6 carbon atoms and the paraffinic and olefinic isomers thereof. For example, the hydrocarbon-containing gas can comprise less than 30, 25, 15, 10, 5, or 2 mole percent of C₆₊ compounds.

Moreover, the hydrocarbon-containing gas can comprise some amount of impurities such as, for example, benzene, toluene, and xylene (“BTX”). For example, the hydrocarbon-containing gas can comprise less than 30, 25, 15, 10, 5, 2, or 1 mole percent of BTX components.

As shown in FIG. 1, the hydrocarbon-containing gas in conduit 110 may initially be routed to a pretreatment zone 16, wherein one or more undesirable constituents may be removed from the gas prior to cooling. In one or more embodiments, the pretreatment zone 16 can include one or more vapor-liquid separation vessels (not shown) for removing liquid water or hydrocarbon components from the feed gas. Optionally, the pretreatment zone 16 can include one or more gas removal zones (not shown), such as, for example, an amine unit or molecular sieve, for removing carbon dioxide and/or sulfur-containing compounds from the gas stream in conduit 110.

The treated gas stream exiting pretreatment zone 16 via conduit 112 can then be routed to a dehydration unit 18, wherein substantially all of the residual water can be removed from the feed gas stream. Dehydration unit 18 can utilize any known water removal system, such as, for example, beds of molecular sieve. Once dried, the gas stream in conduit 114 can have a temperature of at least 5, 10, or 15° C. and/or not more than 50, 45, or 40° C. More particularly, the gas stream in conduit 114 can have a temperature in the range of 5 to 50° C., 10 to 45° C., or 15 to 40° C. Additionally or alternatively, the gas stream in conduit 114 can have a pressure of at least 1.5, 2.5, 3.5, or 4.0 and/or not more than 9.0, 8.0, 7.5, or 7 MPa. More particularly, the gas stream in conduit 114 can have a pressure in the range of 1.5 to 9.0, 2.5 to 8.0, 3.5 to 7.5, or 4.0 to 7.0 MPa.

As shown in FIG. 1, the hydrocarbon-containing feed stream in conduit 114 can be introduced into a first cooling pass 22 in the first cooling zone 20 of the first refrigeration system 12. As described further below, the first refrigeration system 12 can be any heat exchanger or series of heat exchangers operable to cool and at least partially condense the feed gas stream in conduit 114 via indirect heat exchange with a first mixed refrigerant. In one or more embodiments, the first refrigeration system 12 can be a brazed aluminum heat exchanger comprising a plurality of cooling and warming passes (e.g., cores) disposed therein for facilitating indirect heat exchange between one or more process streams and one or more refrigerant streams.

The hydrocarbon-containing feed gas stream passing through cooling pass 22 of first cooling zone 20 can be cooled via indirect heat exchange with the first mixed refrigerant in refrigerant warming pass 24, which is described below in further detail. As used herein, the term “mixed refrigerant” refers to a refrigerant composition comprising two or more constituents.

The gas stream in conduit 116 can then be introduced into a second cooling pass 28 in the second cooling zone 26 of the first refrigeration system 12. In various embodiments, the hydrocarbon-containing feed gas stream passing through cooling pass 28 of second cooling zone 26 can be cooled via indirect heat exchange with the first mixed refrigerant in refrigerant warming pass 30, which is described below in further detail. In certain embodiments, at least a portion of the methane component in the feed gas stream can be condensed out of the vapor phase during cooling to thereby provide a cooled, two-phase fluid stream in conduit 118. Alternatively, in certain embodiments, the second cooling zone 26 will not condense the methane component in the feed gas stream and the resulting fluid stream in conduit 118 will be a single phase vapor stream.

The gas stream in conduit 118 can then be introduced into a third cooling pass 34 in the third cooling zone 32 of the first refrigeration system 12. In certain embodiments, the hydrocarbon-containing feed gas stream passing through cooling pass 34 of third cooling zone 32 can be cooled via indirect heat exchange with the first mixed refrigerant in refrigerant warming pass 36, which is described below in further detail. In various embodiments, at least a portion of the methane component in the feed gas stream can be condensed out of the vapor phase to thereby provide a cooled, two-phase fluid stream in conduit 120. In one or more embodiments, at least 5, 10, 25, 50, 60, 70, 80, or 90 percent of the total amount of methane introduced into first refrigeration system 12 can be condensed upon exiting the third cooling zone 32. Alternatively, in certain embodiments, the third cooling zone 32 will not condense the methane component in the feed gas stream and the resulting fluid stream in conduit 120 will be a single phase vapor stream.

As shown in FIG. 1, the hydrocarbon-containing feed stream in conduit 120 can then be introduced into a cooling pass 40 in the single cooling zone 38 of the second refrigeration system 14. As described further below, the second refrigeration system 14 can be a heat exchanger operable to condense and subcool the feed gas stream in conduit 120 via indirect heat exchange with a second mixed refrigerant. In one or more embodiments, the second refrigeration system 14 can be a brazed aluminum heat exchanger comprising a plurality of cooling and warming passes (e.g., cores) disposed therein for facilitating indirect heat exchange between one or more process streams and one or more refrigerant streams.

Although not depicted in FIGS. 1-7, in various embodiments, the first refrigeration system 12 and the second refrigeration system 14 can be contained in the same heat exchanger and each of the above-mentioned cooling zones (20, 26, 32, and 38) can be connected in series in a single core within this heat exchanger. Furthermore, although FIGS. 1-7 depict physical conduits between the cooling zones (20, 26, 32, and 38), one skilled in the art would readily appreciate that there could be embodiments where no physical conduits exist between the cooling zones (20, 26, 32, and 38), especially in embodiments where the cooling zones (20, 26, 32, and 38) are connected in series.

The hydrocarbon-containing feed gas stream passing through cooling pass 40 of cooling zone 38 can be condensed and subcooled via indirect heat exchange with the second mixed refrigerant in refrigerant warming pass 42, which is described below in further detail.

Upon leaving the second refrigeration system 14, the subcooled feed stream in conduit 122 can then be expanded via passage through an expansion device 44, wherein the pressure of the stream can be reduced. The expansion device 44 can comprise any suitable expansion device, such as, for example, a Joule-Thomson valve or a hydraulic turbine. Although illustrated in FIG. 1 as comprising a single device 44, it should be understood that any suitable number of expansion devices can be employed. In certain embodiments, the expansion can be a substantially isenthalpic expansion or isentropic expansion. As used herein, the term “substantially isenthalpic” refers to an expansion or flashing step carried out such that less than 1 percent of the total work generated during the expansion is transferred from the fluid to the surrounding environment. As used herein, “isentropic” expansion refers to an expansion or flashing step in which a majority or substantially all of the work generated during the expansion is transferred to the surrounding environment.

The expanded stream in conduit 124 can be regulated by valve 46. The cooled stream exiting valve 46 via conduit 126 can be an LNG-enriched product. As used herein, “LNG-enriched” means that the particular composition comprises at least 50 mole percent of methane. The LNG-enriched product in conduit 126 can have a temperature colder than −120, −130, −140, or −145° C. and/or warmer than −195, −190, −180, or −165° C. More particularly, the LNG-enriched product in conduit 126 can have a temperature in the range of −120 to −195° C., −130 to −190° C., −140 to −180° C., or −145 to −165° C.

Turning back to FIG. 1, the first refrigeration system 12 and the first closed-loop mixed refrigeration cycle are now described below in further detail. As shown on FIG. 1, the first refrigeration system 12 contains three cooling zones (20, 26, and 32), wherein the first closed-loop mixed refrigeration cycle is at least partially disposed therein.

The first closed-loop mixed refrigeration cycle comprises the first mixed refrigerant and is depicted in FIG. 1 as follows. Upon leaving refrigerant warming pass 24 in the first cooling zone 20, the gaseous first mixed refrigerant in conduit 128 is transferred to a compressor system 48 comprising a first compressor stage 54, a second compressor stage 52, and a third compressor stage 50.

In various embodiments, the gaseous first mixed refrigerant in conduit 128 can be at a pressure of at least 1.5, 2.0, or 2.7 MPa and/or not more than 5.0, 4.0, or 3.5 MPa. More particularly, the gaseous first mixed refrigerant in conduit 128 can be at a pressure in the range of 1.5 to 5.0 MPa, 2.0 to 4.0 MPa, or 2.7 to 3.5 MPa. Additionally or alternatively, the gaseous first mixed refrigerant in conduit 128 can be at a temperature lower than 50, 35, or 25° C. and/or warmer than −40, −30, or −20° C. More particularly, the gaseous first mixed refrigerant in conduit 128 can be at a temperature in the range of −40 to 50° C., −30 to 35° C., or −20 to 25° C.

Although depicted as containing only three stages in FIG. 1, one skilled in the art would readily appreciate that the compressor 48 could be modified to include more or less stages as necessary. In various embodiments, the compressor system 48 can comprise an axial compressor, centrifugal compressor, reciprocating compressor, screw compressor, or a combination thereof. Additionally, the compressor system 48 can be driven by a steam turbine, gas turbine, electric motor, or combinations thereof.

In various embodiments, refrigerant may leak through the seals of the compressor 48. In such embodiments, rather than vent the lost refrigerant, a seal gas recovery process can be utilized that recovers at least a portion of the refrigerant and returns it to the refrigeration loop. A seal gas recovery process is described in U.S. Pat. No. 8,066,023, which is incorporated herein by reference in its entirety. For example, the compressor 48 can be fitted with a venturi (not shown) for retaining any seal gas leaked from the compressor.

The gaseous first mixed refrigerant in conduit 128 can be introduced into the third compressor stage 50. In various embodiments, the third compressor stage 50 can compress the gaseous first mixed refrigerant to a pressure of at least 2.5, 4.0, or 4.8 MPa and/or not more than 8.0, 7.0, or 6.3 MPa. More particularly, the third compressor stage 50 can compress the gaseous first mixed refrigerant to a pressure in the range of 2.5 to 8.0 MPa, 4.0 to 7.0 MPa, or 4.8 to 6.3 MPa.

The compressed first mixed refrigerant is transferred via conduit 130 to discharge cooler 56, wherein the stream can be cooled to an approach with ambient temperatures and fully condensed via indirect heat exchange with an external cooling medium (e.g., cooling water or air). As used herein, “fully condensed” means that the identified stream comprises less than 1.0 mole percent of vapor. In one or more embodiments, the fully condensed stream can comprise less than 0.5, 0.1, 0.05, or 0.001 mole percent of vapor. In various embodiments, the first mixed refrigerant must be a liquid at the cooler discharge pressure.

Upon leaving the discharge cooler 56 via conduit 132, the fully condensed first mixed refrigerant is introduced into cooling pass 58 in the first cooling zone 20. In various embodiments, the fully condensed first mixed refrigerant in conduit 132 can be at a pressure of at least 2.5, 4.0, or 4.8 MPa and/or not more than 8.0, 7.0, or 6.3 MPa. More particularly, the fully condensed first mixed refrigerant in conduit 132 can be at a pressure in the range of 2.5 to 8.0 MPa, 4.0 to 7.0 MPa, or 4.8 to 6.3 MPa. Additionally or alternatively, the fully condensed first mixed refrigerant in conduit 132 can be at an approach to ambient temperatures.

In cooling pass 58, the fully condensed first mixed refrigerant can be subcooled via indirect heat exchange with the first mixed refrigerant in refrigerant warming pass 24, which is described further below.

Upon leaving cooling pass 58 via conduit 134, at least a portion of the stream can be routed via conduit 136 to expansion device 60, wherein the pressure of the stream can be reduced, thereby cooling and, in some embodiments, at least partially vaporizing the refrigerant stream. The expansion device 60 can comprise any suitable expansion device, such as, for example, a Joule-Thomson valve or a hydraulic turbine. Although illustrated in FIG. 1 as comprising a single device 60, it should be understood that any suitable number of expansion devices can be employed. In certain embodiments, the expansion can be a substantially isenthalpic expansion or isentropic expansion.

Prior to expansion, the fully condensed first mixed refrigerant in conduit 136 can be at a pressure of at least 2.5, 4.0, or 4.8 MPa and/or not more than 8.0, 7.0, or 6.3 MPa. More particularly, the fully condensed first mixed refrigerant in conduit 136 can be at a pressure in the range of 2.5 to 8.0, 4.0 to 7.0, or 4.8 to 6.3 MPa. Additionally or alternatively, the fully condensed first mixed refrigerant in conduit 136 can be at a temperature lower than 30, 25, or 15° C. and/or warmer than −40, −30, or −5° C. More particularly, the fully condensed first mixed refrigerant in conduit 136 can be at a temperature in the range of −40 to 30° C., −30 to 25° C., or −5 to 15° C.

In various embodiments, the fully condensed first mixed refrigerant is not subjected to phase separation prior to or following the expansion step. As used herein, “phase separation” involves separating a two-phase stream, generally containing liquid and vapor phases, into their respective phases.

The expanded first mixed refrigerant is introduced into refrigerant warming pass 24 via conduit 138, wherein the expanded first mixed refrigerant can be vaporized in order to provide refrigeration to the first cooling zone 20.

In various embodiments, the expanded first mixed refrigerant in conduit 138 can comprise less than 5, 3, 1, 0.5, or 0.1 mole percent of a vapor phase. Furthermore, in certain embodiments, the expanded first mixed refrigerant in conduit 138 can be at a pressure of at least 1.5, 2.0, or 2.7 MPa and/or not more than 5.0, 4.0, or 3.5 MPa. More particularly, the expanded first mixed refrigerant in conduit 138 can be at a pressure in the range of 1.5 to 5.0 MPa, 2.0 to 4.0 MPa, or 2.7 to 3.5 MPa. Additionally or alternatively, the expanded first mixed refrigerant in conduit 138 can be at a temperature lower than 30, 25, or 15° C. and/or warmer than −40, −30, or −5° C. More particularly, the expanded first mixed refrigerant in conduit 138 can be at a temperature in the range of −40 to 30° C., −30 to 25° C., or −5 to 15° C.

The vaporized, gaseous first mixed refrigerant leaves refrigerant warming pass 24 via conduit 128 as described above.

Turning again to FIG. 1, at least a portion of the fully condensed first mixed refrigerant in conduit 134 is directed to cooling pass 62 in the second cooling zone 26. In cooling pass 62, the fully condensed first mixed refrigerant can be further subcooled via indirect heat exchange with the first mixed refrigerant in refrigerant warming pass 30, which is described further below.

Upon leaving cooling pass 62 via conduit 140, at least a portion of the stream can be routed via conduit 142 to expansion device 64, wherein the pressure of the stream can be reduced, thereby cooling and, in some embodiments, at least partially vaporizing the refrigerant stream. The expansion device 64 can comprise any suitable expansion device, such as, for example, a Joule-Thomson valve or a hydraulic turbine. Although illustrated in FIG. 1 as comprising a single device 64, it should be understood that any suitable number of expansion devices can be employed. In certain embodiments, the expansion can be a substantially isenthalpic expansion or isentropic expansion. In various embodiments, the fully condensed first mixed refrigerant is not subjected to phase separation prior to or following the expansion step.

Prior to expansion, the fully condensed first mixed refrigerant in conduit 142 can be at a pressure of at least 2.5, 4.0, or 4.8 MPa and/or not more than 8.0, 7.0, or 6.3 MPa. More particularly, the fully condensed first mixed refrigerant in conduit 142 can be at a pressure in the range of 2.5 to 8.0, 4.0 to 7.0, or 4.8 to 6.3 MPa. Additionally or alternatively, the fully condensed first mixed refrigerant in conduit 142 can be at a temperature lower than 0, −10, or −25° C. and/or warmer than −100, −75, or −50° C. More particularly, the fully condensed first mixed refrigerant in conduit 142 can be at a temperature in the range of −100 to 0° C., −75 to −10° C., or −50 to −25° C.

The expanded first mixed refrigerant is introduced into refrigerant warming pass 30 via conduit 144, wherein the expanded first mixed refrigerant is vaporized in order to provide refrigeration to the second cooling zone 26. In various embodiments, the expanded first mixed refrigerant in conduit 144 can comprise less than 5, 4, 3, 2, 1, or 0.1 mole percent of a vapor phase. Furthermore, in certain embodiments, the expanded first mixed refrigerant in conduit 144 can be at a pressure of at least 0.3, 0.5, or 0.65 MPa and/or not more than 2.0, 1.7, or 1.4 MPa. More particularly, the expanded first mixed refrigerant in conduit 144 can be at a pressure in the range of 0.3 to 2.0 MPa, 0.5 to 1.7 MPa, or 0.65 to 1.4 MPa. Additionally or alternatively, the expanded first mixed refrigerant in conduit 144 can be at a temperature lower than 0, −10, or −25° C. and/or warmer than −100, −75, or −50° C. More particularly, the expanded first mixed refrigerant in conduit 144 can be at a temperature in the range of −100 to 0° C., −75 to −10° C., or −50 to −25° C.

The vaporized, gaseous first mixed refrigerant leaves refrigerant warming pass 30 via conduit 146 and can be introduced into the second stage of the compressor 52. In various embodiments, the gaseous first mixed refrigerant in conduit 146 can be at a pressure of at least 0.3, 0.5, or 0.65 MPa and/or not more than 2.0, 1.7, or 1.4 MPa. More particularly, the gaseous first mixed refrigerant in conduit 146 can be at a pressure in the range of 0.3 to 2.0 MPa, 0.5 to 1.7 MPa, or 0.65 to 1.4 MPa. Additionally or alternatively, the gaseous first mixed refrigerant in conduit 146 can be at a temperature lower than 30, 25, or 15° C. and/or warmer than −40, −30, or −5° C. More particularly, the gaseous first mixed refrigerant in conduit 146 can be at a temperature in the range of −40 to 30° C., −30 to 25° C., or −5 to 15° C.

In various embodiments, the second compressor stage 52 can compress the gaseous first mixed refrigerant to a pressure of at least 1.5, 2.0 or 2.7 MPa and/or not more than 5.0, 4.0, or 3.5 MPa. More particularly, the second compressor stage 52 can compress the gaseous first mixed refrigerant to a pressure in the range of 1.5 to 5.0 MPa, 2.0 to 4.0 MPa, or 2.7 to 3.5 MPa.

The compressed first mixed refrigerant from the second stage of the compressor 52 is transferred via conduit 148 to interstage cooler 66, wherein the stream can be cooled via indirect heat exchange with an external cooling medium (e.g., cooling water or air). Upon leaving the interstage cooler 66 via conduit 150, the compressed stream in conduit 150 can be introduced into conduit 128, where it can be directed to further compression in the third compressor stage 50 as described above.

Turning again to FIG. 1, at least a portion of the fully condensed first mixed refrigerant in conduit 140 is directed to cooling pass 68 in the third cooling zone 32. In cooling pass 68, the fully condensed first mixed refrigerant can be further subcooled via indirect heat exchange with the first mixed refrigerant in refrigerant warming pass 36, which is described further below.

Upon leaving cooling pass 68 via conduit 152, the cooled stream can be routed to expansion device 70, wherein the pressure of the stream can be reduced, thereby cooling and at least partially vaporizing the refrigerant stream. The expansion device 70 can comprise any suitable expansion device, such as, for example, a Joule-Thomson valve or a hydraulic turbine. Although illustrated in FIG. 1 as comprising a single device 70, it should be understood that any suitable number of expansion devices can be employed. In certain embodiments, the expansion can be a substantially isenthalpic expansion or isentropic expansion. In various embodiments, the fully condensed first mixed refrigerant is not subjected to phase separation prior to or following the expansion step.

Prior to expansion, the fully condensed first mixed refrigerant in conduit 152 can be at a pressure of at least 2.5, 4.0, or 4.8 MPa and/or not more than 8.0, 7.0, or 6.3 MPa. More particularly, the fully condensed first mixed refrigerant in conduit 152 can be at a pressure in the range of 2.5 to 8.0, 4.0 to 7.0, or 4.8 to 6.3 MPa. Additionally or alternatively, the fully condensed first mixed refrigerant in conduit 152 can be at a temperature lower than −20, −40, or −60° C. and/or warmer than −120, −90, or −75° C. More particularly, the fully condensed first mixed refrigerant in conduit 152 can be at a temperature in the range of −120 to −20° C., −90 to −40° C., or −75 to −60° C.

The expanded first mixed refrigerant is introduced into refrigerant warming pass 36 via conduit 154, wherein the expanded first mixed refrigerant is vaporized in order to provide refrigeration to the third cooling zone 32. In various embodiments, the expanded first mixed refrigerant in conduit 154 can comprise less than 10, 7, 6, 4, 2, 1, or 0.5 mole percent of a vapor phase. Furthermore, in certain embodiments, the expanded first mixed refrigerant in conduit 154 can be at a pressure of at least 0.1, 0.15, or 0.2 MPa and/or not more than 2.0, 1.5, or 0.5 MPa. More particularly, the expanded first mixed refrigerant in conduit 154 can be at a pressure in the range of 0.1 to 2.0 MPa, 0.15 to 1.5 MPa, or 0.2 to 0.5 MPa. Additionally or alternatively, the expanded first mixed refrigerant in conduit 154 can be at a temperature lower than −20, −40, or −60° C. and/or warmer than −120, −90, or −75° C. More particularly, the expanded first mixed refrigerant in conduit 154 can be at a temperature in the range of −120 to −20° C., −90 to −40° C., or −75 to −60° C.

The vaporized, gaseous first mixed refrigerant leaves refrigerant warming pass 36 via conduit 156 and can be introduced into the first stage of the compressor 54. In various embodiments, the gaseous first mixed refrigerant in conduit 156 can be at a pressure of at least 0.1, 0.15, or 0.2 MPa and/or not more than 2.0, 1.5, or 0.5 MPa. More particularly, the gaseous first mixed refrigerant in conduit 156 can be at a pressure in the range of 0.1 to 2.0 MPa, 0.15 to 1.5 MPa, or 0.2 to 0.5 MPa. Additionally or alternatively, the gaseous first mixed refrigerant in conduit 156 can be at a temperature lower than 0, −10, or −25° C. and/or warmer than −100, −75, or −50° C. More particularly, the gaseous first mixed refrigerant in conduit 156 can be at a temperature in the range of −100 to 0° C., −75 to −10° C., or −50 to −25° C.

Upon leaving the first compressor stage 54 via conduit 158, the compressed stream in conduit 158 can be introduced into conduit 146, where it can be directed to further compression in the second compressor stage 52 and third compressor stage 50 as described above. In various embodiments, the first compressor stage 54 can compress the gaseous first mixed refrigerant to a pressure of at least 0.3, 0.5, or 0.65 MPa and/or not more than 2.0, 1.7, or 1.4 MPa. More particularly, the first compressor stage 54 can compress the gaseous first mixed refrigerant to a pressure in the range of 0.3 to 2.0 MPa, 0.5 to 1.7 MPa, or 0.65 to 1.4 MPa.

In various embodiments, and as depicted in FIG. 1, the first refrigeration system 12 and the first closed-loop mixed refrigeration cycle does not contain a phase separator. As used herein, a “phase separator” is understood to encompass any device designed exclusively to separate a partially condensed stream into liquid and vapor fractions. Consequently, this would not include, for example, suction drums and surge drums.

In certain embodiments, conduits 136, 138, 142, 144, 152, and 154 in FIG. 1, when physically present, can be located outside of their respective cooling zones (20, 26, and 32). In such embodiments, conduits 136, 138, 142, 144, 152, and 154 could be located outside the heat exchanger or heat exchangers that contain the respective cooling zones (20, 26, and 32).

The first mixed refrigerant can comprise two or more constituents selected from the group consisting of nitrogen, methane, ethylene, ethane, propylene, propane, isobutane, n-butane, isopentane, n-pentane, and combinations thereof. In some embodiments, the first mixed refrigerant can comprise at least two compounds selected from the group consisting of hydrocarbons containing from 2 to 4 carbon atoms. In certain embodiments, the first mixed refrigerant can have a bubble point pressure between 2.5 to 5.65 MPa at around ambient temperatures.

In some embodiments of the present invention, it may be desirable to adjust the composition of the first mixed refrigerant to thereby alter its cooling curve and, therefore, its refrigeration potential. Such a modification may be utilized to accommodate, for example, changes in composition and/or flow rate of the feed gas stream introduced into LNG recovery facility 10. In one embodiment, the composition of the first mixed refrigerant can be adjusted such that the heating curve of the vaporizing refrigerant more closely matches the cooling curve of the feed gas stream and warm refrigerant. One method for such curve matching is described in detail in U.S. Pat. No. 4,033,735, the disclosure of which is incorporated herein by reference in its entirety.

Turning once again to FIG. 1, the second refrigeration system 14 and the second closed-loop mixed refrigeration cycle are now described in further detail. As shown on FIG. 1, the second refrigeration system 14 contains a single cooling zone 38, wherein the second closed-loop mixed refrigeration cycle is at least partially disposed therein. As used herein, “single cooling zone” means that the system comprises only one zone wherein the feed stream is cooled via indirect heat exchange with a single coolant. In such embodiments, the identified system will not contain any other cooling zones. In certain embodiments, the single coolant can comprise the expanded first mixed refrigerant or the expanded second mixed refrigerant. In various embodiments, the second refrigeration system 12 comprises, consists essentially of, or consists of a single cooling zone.

The second closed-loop mixed refrigeration cycle comprises the second mixed refrigerant and is depicted in FIG. 1 as follows. Upon leaving refrigerant warming pass 42 in the cooling zone 38, the gaseous second mixed refrigerant in conduit 160 is transferred to a compressor system 72 comprising a first compressor stage 74 and a second compressor stage 76. In various embodiments, the compressor 72 may be configured to recover seal gas as previously described in regard to compressor 48. Thus, in certain embodiments, the compressor 72 may contain a venturi (not shown) designed to retain seal gas leaked outside the compressor.

In various embodiments, the gaseous second mixed refrigerant in conduit 160 is at a pressure in the range of 0.1, 0.15, or 0.2 MPa and/or not more than 2.0, 1.5, or 0.5 MPa. More particularly, the gaseous second mixed refrigerant in conduit 160 can be at a pressure in the range of 0.1 to 2.0 MPa, 0.15 to 1.5 MPa, or 0.2 to 0.5 MPa. Additionally or alternatively, the gaseous second mixed refrigerant in conduit 160 is at a temperature lower than −20, −40, or −60° C. and/or warmer than −120, −90, or −75° C. More particularly, the gaseous second mixed refrigerant in conduit 160 can be at a temperature in the range of −120 to −20° C., −90 to −40° C., or −75 to −60° C.

Although depicted as containing only two stages in FIG. 1, one skilled in the art would readily appreciate that the compressor 72 could be modified to include more or less stages as necessary. In various embodiments, the compressor system 72 can comprise an axial compressor, centrifugal compressor, reciprocating compressor, screw compressor, or a combination thereof. Additionally, the compressor system 72 can be driven by a steam turbine, gas turbine, electric motor, or combinations thereof.

The gaseous second mixed refrigerant in conduit 160 is introduced to the first compressor stage 74 and then transferred via conduit 162 to interstage cooler 78, wherein the stream can be cooled to an approach with ambient temperature via indirect heat exchange with an external cooling medium (e.g., cooling water or air). In various embodiments, the first compressor stage 74 can compress the gaseous second mixed refrigerant to a pressure of at least 0.3, 0.5, or 0.65 MPa and/or not more than 3.0, 2.5, or 2.0 MPa. More particularly, the first compressor stage 74 can compress the gaseous second mixed refrigerant to a pressure in the range of 0.3 to 3.0 MPa, 0.5 to 2.5 MPa, or 0.65 to 2.0 MPa.

The cooled second mixed refrigerant can then be introduced into the second compressor stage 76 via conduit 164, wherein the second mixed refrigerant is further compressed. In various embodiments, the second compressor stage 76 can compress the gaseous second mixed refrigerant to a pressure of at least 2.5, 4.0, or 4.8 and/or not more than 8.0, 7.0, or 6.0 MPa. More particularly, the second compressor stage 76 can compress the gaseous second mixed refrigerant to a pressure in the range of 2.5 to 8.0 MPa, 4.0 to 7.0 MPa, or 4.8 to 6.0 MPa.

The compressed second mixed refrigerant is then introduced into discharge cooler 80 via conduit 166, wherein the stream can be further cooled to an approach with ambient temperature via indirect heat exchange with an external cooling medium (e.g., cooling water or air).

The compressed second mixed refrigerant in conduit 168 is then introduced into cooling pass 82 in the first cooling zone 20 of the first refrigeration system 12. In various embodiments, the compressed second mixed refrigerant in conduit 168 can be at a pressure of at least 2.5, 4.0, or 4.8 MPa and/or not more than 8.0, 7.0, or 6.0 MPa. More particularly, the compressed second mixed refrigerant in conduit 168 can be at a pressure in the range of 2.5 to 8.0 MPa, 4.0 to 7.0 MPa, or 4.8 to 6.0 MPa. Additionally or alternatively, the compressed second mixed refrigerant in conduit 168 can be at or near ambient temperatures.

In cooling pass 82, the second mixed refrigerant can be further cooled via indirect heat exchange with the first mixed refrigerant in refrigerant warming pass 24. While in cooling pass 82, the second mixed refrigerant can be cooled to a temperature below the dew point of the refrigerant mixture.

The cooled second mixed refrigerant in conduit 170 is then introduced into cooling pass 84 in the second cooling zone 26 of the first refrigeration system 12. In cooling pass 84, the second mixed refrigerant can be further cooled via indirect heat exchange with the first mixed refrigerant in refrigerant warming pass 30. While in cooling pass 84, the second mixed refrigerant can be cooled to a temperature below the dew point of the refrigerant mixture.

The cooled second mixed refrigerant in conduit 172 is then introduced into cooling pass 86 in the third cooling zone 32 of the first refrigeration system 12. In cooling pass 86, the second mixed refrigerant can be further cooled via indirect heat exchange with the first mixed refrigerant in refrigerant warming pass 36. While in cooling pass 86, the second mixed refrigerant can be cooled to a temperature below the bubble point of the refrigerant mixture.

Upon leaving the first refrigeration system 12 via conduit 174, the second mixed refrigerant in conduit 174 is fully condensed. The fully condensed second mixed refrigerant in conduit 174 can then be introduced into cooling pass 88 in cooling zone 38 of the second refrigeration system 14.

Upon leaving cooling pass 88 via conduit 176, the subcooled second mixed refrigerant stream can be routed to expansion device 90, wherein the pressure of the stream can be reduced, thereby cooling and vaporizing the refrigerant stream. Prior to expansion, the fully condensed second mixed refrigerant in conduit 176 can be at a pressure of at least 2.5, 4.0, or 4.8 MPa and/or not more than 8.0, 7.0, or 6.0 MPa. More particularly, the fully condensed second mixed refrigerant in conduit 176 can be at a pressure in the range of 2.5 to 8.0, 4.0 to 7.0, or 4.8 to 6.0 MPa. Additionally or alternatively, the fully condensed second mixed refrigerant in conduit 176 can be at a temperature colder than −120, −130, −140, or −145° C. and/or warmer than −195, −190, −180, or −165° C. More particularly, the fully condensed second mixed refrigerant in conduit 176 can be at a temperature in the range of −120 to −195° C., −130 to −190° C., −140 to −180° C., or −145 to −165° C.

The expansion device 90 can comprise any suitable expansion device, such as, for example, a Joule-Thomson valve or a hydraulic turbine. Although illustrated in FIG. 1 as comprising a single device 90, it should be understood that any suitable number of expansion devices can be employed. In certain embodiments, the expansion can be a substantially isenthalpic expansion or isentropic expansion.

The expanded stream in conduit 178 can be regulated by valve 92. In various embodiments, the expanded stream in conduit 178 can comprise less than 15, 10, 8, 6, 2, or 1 mole percent of a vapor phase. Furthermore, in certain embodiments, the expanded stream in conduit 178 can be at a pressure of at least 0.3, 0.5, or 0.65 MPa and/or not more than 3.0, 2.0, or 1.4 MPa. More particularly, the expanded stream in conduit 178 can be at a pressure in the range of 0.3 to 3.0 MPa, 0.5 to 2.0 MPa, or 0.65 to 1.4 MPa. Additionally or alternatively, the expanded stream in conduit 178 can be at a temperature colder than −120, −130, −140, or −145° C. and/or warmer than −195, −190, −180, or −165° C. More particularly, the expanded stream in conduit 178 can be at a temperature in the range of −120 to −195° C., −130 to −190° C., −140 to −180° C., or −145 to −165° C.

The expanded second mixed refrigerant in conduit 180 is then introduced into refrigerant warming pass 42, wherein the expanded second mixed refrigerant is vaporized in order to provide refrigeration to the cooling zone 38. In various embodiments, the expanded stream in conduit 180 can comprise less than 15, 10, 8, 6, or 2 mole percent of a vapor phase. In one or more embodiments, the expanded second mixed refrigerant in conduit 180 can be introduced at a pressure in the range of 0.1, 0.15, or 0.2 MPa and/or not more than 2.0, 1.5, or 0.5 MPa. More particularly, the expanded second mixed refrigerant in conduit 180 can be introduced at a pressure in the range of 0.1 to 2.0 MPa, 0.15 to 1.5 MPa, or 0.2 to 0.5 MPa.

In certain embodiments, conduits 174, 176, 178, and 180 can be located outside the cooling zone 38. In such embodiments, conduits 174, 176, 178, and 180 could be located outside the heat exchanger that contains cooling zone 38.

The gaseous second mixed refrigerant in conduit 160 is then compressed and recycled in the process described above. In various embodiments, the fully condensed second mixed refrigerant is not subjected to phase separation prior to or following the expansion step.

In various embodiments, and as depicted in FIG. 1, the second refrigeration system 14 and the second closed-loop mixed refrigeration cycle does not contain a phase separator.

The second mixed refrigerant can comprise two or more constituents selected from the group consisting of nitrogen, methane, ethylene, ethane, propylene, propane, isobutane, n-butane, isopentane, n-pentane, and combinations thereof. In some embodiments, the second mixed refrigerant can comprise at least two compounds selected from the group consisting of nitrogen and hydrocarbons containing from 1 to 3 carbon atoms. In various embodiments, the second mixed refrigerant will have a bubble point temperature that is lower than the bubble point temperature of the first mixed refrigerant at a given pressure. In certain embodiments, the second mixed refrigerant can have a bubble point pressure between 2.5 to 6.1 MPa at temperatures between −60 to −75° C.

In some embodiments of the present invention, it may be desirable to adjust the composition of the second mixed refrigerant to thereby alter its cooling curve and, therefore, its refrigeration potential. Such a modification may be utilized to accommodate, for example, changes in composition and/or flow rate of the feed gas stream introduced into LNG recovery facility 10. In one embodiment, the composition of the second mixed refrigerant can be adjusted such that the heating curve of the vaporizing refrigerant more closely matches the cooling curve of the feed gas stream and warm refrigerant.

It should be noted that the conduits depicted between the cooling zones (20, 26, 32, and 38) in FIG. 1 are shown for illustrative purposes only and, in certain embodiments, a physical conduit may not be present where each conduit is shown in FIG. 1.

While FIG. 1 depicts one embodiment of the present processes and systems, other embodiments are envisioned, such as those depicted in FIGS. 2-7, which can incorporate a turboexpander 94, compressor 96 operably connected to the turboexpander 94, and a heavies separator 98. It should be noted that all common system components found in FIGS. 1-7 are all marked accordingly using the same numerals. For example, the first refrigeration system 12 and second refrigeration 14 are both consistently labeled throughout FIGS. 1-7. Furthermore, the system components in FIGS. 1-7 are expected to function in the same or substantially similar manner, unless otherwise noted. The only labeling difference between FIGS. 1-7 is that the conduits therein are marked up in accordance with their respective figure and embodiment. For example, the respective conduits in FIG. 2 are labeled 2XX, while the respective conduits in FIG. 3 are labeled 3XX (where “X” represents a numeral). The conduits in FIGS. 1-7 function in the same manner throughout (i.e., transferring their respective stream) unless otherwise noted.

In FIG. 2, an LNG recovery facility 10 is depicted that contains a turboexpander 94 operably connected via conduit 220 to the third cooling zone 32 of the first refrigeration system 12. A turboexpander is further described in U.S. Pat. No. 6,367,286, which is incorporated herein by reference in its entirety.

As shown in FIG. 2, at least a portion of the hydrocarbon-containing feed gas stream passing through the cooling pass 34 of third cooling zone 32 can be directed via conduit 220 to the turboexpander 94, where it can be expanded into a two-phase stream. As a result of the expansion, the temperature of the flashed or expanded fluid stream in conduit 222 can be at least 2, 5, or 10° C. and/or not more than 50, 40, or 30° C. lower than the temperature of the stream in conduit 220. Furthermore, the pressure of the flashed or expanded fluid stream in conduit 222 can be at least 0.1, 0.2, or 0.3 and/or not more than 5.0, 4.0, or 3.0 MPa lower than the pressure of the stream in conduit 220. In certain embodiments, the expansion can be substantially isentropic. Although not depicted in FIG. 2, a suction drum may be in fluid communication between the turboexpander 94 and third cooling zone 32 in certain embodiments.

Furthermore, the turboexpander 94 is connected to a compressor 96 via shaft 95. The compressor 96 can be at least partially driven from the work derived from the turboexpander 94. As described below, the compressor 96 is configured to at least partially compress the overhead fraction coming from the separator 98. In various embodiments, the compressor 96 can comprise an axial compressor, centrifugal compressor, reciprocating compressor, screw compressor, or a combination thereof. Additionally, the compressor 96 can be driven by a steam turbine, gas turbine, electric motor, or combinations thereof.

In various embodiments, the compressor 96 may be configured to recover seal gas as previously described in regard to compressor 48. Thus, in certain embodiments, the compressor 96 may contain a venturi (not shown) designed to retain seal gas leaked outside the compressor.

As shown in FIG. 2, the expanded two-phase stream in conduit 222 is directed to the separator 98 that separates the expanded stream into a liquid heavy fraction that is methane-poor (conduit 224) and an overhead vapor fraction that is methane-rich (conduit 226). As used herein, “methane-poor” and “methane-rich” refer to the methane content of the separated components relative to the methane content of the original component from which the separated components are derived. Thus, a methane-rich component contains a greater mole percentage of methane than the component from which it is derived, while a methane-poor component contains a lesser mole percentage of methane than the component from which it is derived. In the present case, the methane-poor bottom stream contains a lower mole percentage of methane compared to the stream from conduit 222, while methane-rich overhead stream contains a higher mole percentage of methane compared to the stream from conduit 222. The amounts of the methane-poor bottom stream and the methane-rich overhead stream can vary depending on the contents of the hydrocarbon-containing gas and the operating conditions of the separation vessel 98.

The methane-poor bottom stream in conduit 224 can be in the form of a liquid and can contain most of the compounds having six or more carbon atoms originally found in the stream in conduit 222. For example, the methane-poor bottom stream in conduit 224 can comprise at least 70, 80, 90, 95, or 99 percent of the compounds having six or more carbon atoms originally present in the stream from conduit 222.

The methane-rich overhead vapor stream in conduit 226 can comprise a large portion of methane. For example, the methane-rich overhead vapor stream in conduit 226 can comprise at least about 10, 25, 40, or 50 and/or not more than about 99.9, 99, 95, or 85 mole percent of methane. More particularly, the methane-rich overhead vapor stream in conduit 226 can comprise in the range of about 10 to 99.9, 25 to 99, 40 to 95, or 50 to 85 mole percent of methane. Furthermore, the methane-rich overhead vapor stream in conduit 226 can comprise at least 50, 60, 70, 80, 90, 95, 99, or 99.9 percent of the methane originally present in the stream from conduit 222.

The separation vessel 98 can be any suitable vapor-liquid separation vessel and can have any number of actual or theoretical separation stages. In one or more embodiments, separation vessel 98 can comprise a single separation stage, while in other embodiments, the separation vessel 98 can include 2 to 10, 4 to 20, or 6 to 30 actual or theoretical separation stages. When separation vessel 98 is a multistage separation vessel, any suitable type of column internals, such as mist eliminators, mesh pads, vapor-liquid contacting trays, random packing, and/or structured packing, can be used to facilitate heat and/or mass transfer between the vapor and liquid streams. In some embodiments, when separation vessel 98 is a single-stage separation vessel, few or no column internals can be employed.

In various embodiments, the separation vessel 98 can operate at a pressure of at least 1.5, 2.5, 3.5, or 4.5 and/or 9.0, 8.0, 7.0, or 6.0 MPa. More particularly, the separation vessel 98 can operate at a pressure in the range of 1.5 to 9.0, 2.5 to 8.0, 3.5 to 7.0, or 4.5 to 6.0 MPa.

As one skilled in the art would readily appreciate, the temperature in the separation vessel 98 can vary depending on the contents of the hydrocarbon-containing gas introduced into the system and the desired output. In various embodiments, the separation vessel 98 can operate at a temperature colder than 5, 10, or 15° C. and/or warmer than −195, −185, −175, or −160° C. More particularly, the separation vessel 98 can operate at a temperature in the range of 15 to −195° C., 10 to −185° C., 5 to −175° C., or 5 to −160° C.

As shown in FIG. 2, the methane-rich overhead vapor stream in conduit 226 can be directed to compressor 96, which compresses the stream. The compressed stream in conduit 228 is then reintroduced into cooling pass 34 of third cooling zone 32 to be further cooled and condensed as described above in regard to FIG. 1.

It should be noted that the first refrigeration system 12, the second refrigeration system 14, the first closed-loop mixed refrigeration cycle (conduits 238, 240, 242, 244, 246, 248, 250, 252, 254, 256, 258, 260, 262, 264, 266, and 268), and the second closed-loop mixed refrigeration cycle (conduits 270, 272, 274, 276, 278, 280, 282, 284, 286, 288, and 290) depicted in FIG. 2, which were not described above in regard to FIG. 2, function in the same manner as previously described in regard to FIG. 1. The only difference is that the respective conduits in FIG. 2 have been labeled differently to account for the particular system embodiment depicted in FIG. 2. Furthermore, the remaining steps involved in liquefying the hydrocarbon-containing gas not addressed above in regard to FIG. 2 (conduits 210, 212, 214, 216, 218, 230, 232, 234, and 236) function in the same or similar manner as previously described in regard to FIG. 1.

In FIG. 3, an LNG recovery facility 10 is depicted that contains a turboexpander 94 operably connected via conduit 320 to the third cooling zone 32 of the first refrigeration system 12. As shown in FIG. 3, at least a portion of the hydrocarbon-containing feed gas stream passing through the cooling pass 34 of third cooling zone 32 can be directed via conduit 320 to the turboexpander 94, where it can be expanded into a two-phase stream. The turboexpander 94 can operate under the same or similar conditions as previously described in regard to FIG. 2. Although not depicted in FIG. 3, a suction drum may be in fluid communication between the turboexpander 94 and third cooling zone 32 in certain embodiments.

The expanded two-phase stream in conduit 322 is then directed to a separator 98 that separates the expanded stream into a liquid heavy fraction that is methane-poor (conduit 324) and an overhead vapor fraction that is methane-rich (conduit 326). The separator 98 can be the same separation vessel as described previously in regard to FIG. 2 and may function under similar operating conditions. After separation, the overhead vapor fraction in conduit 326 is then reintroduced into cooling pass 34 of third cooling zone 32 to be further cooled and condensed as described above in regard to FIG. 1.

The methane-poor bottom stream in conduit 324 can be in the form of a liquid and can contain most of the compounds having six or more carbon atoms originally found in the stream in conduit 322. For example, the methane-poor bottom stream in conduit 324 can comprise at least 70, 80, 90, 95, or 99 percent of the compounds having six or more carbon atoms originally present in the stream from conduit 322.

The methane-rich overhead vapor stream in conduit 326 can comprise a large portion of methane. For example, the methane-rich overhead vapor stream in conduit 326 can comprise at least about 10, 25, 40, or 50 and/or not more than about 99.9, 99, 95, or 85 mole percent of methane. More particularly, the methane-rich overhead vapor stream in conduit 326 can comprise in the range of about 10 to 99.9, 25 to 99, 40 to 95, or 50 to 85 mole percent of methane. Furthermore, the methane-rich overhead vapor stream in conduit 326 can comprise at least 50, 60, 70, 80, 90, 95, 99, or 99.9 percent of the methane originally present in the stream from conduit 322.

Turning again to FIG. 3, the turboexpander 94 is connected to a compressor 96 via shaft 95. The compressor 96 can be at least partially driven from work derived from the turboexpander 94. As shown in FIG. 3, the vaporized, gaseous first mixed refrigerant leaves refrigerant warming pass 36 in the third cooling zone 32 via conduit 364 and is then introduced into the compressor 96, where it is compressed prior to introduction into the compressor 48. After compression, the compressed stream in conduit 366 is introduced into the first compressor stage 54 and is further treated as discussed above in regard to FIG. 1. Although not depicted in FIG. 3, a suction drum may be in fluid communication between the compressor 96 and warming pass 36.

It should be noted that the first refrigeration system 12, the second refrigeration system 14, and the second closed-loop mixed refrigeration cycle (conduits 370, 372, 374, 376, 378, 380, 382, 384, 386, 388, and 390) depicted in FIG. 3, which were not described above in regard to FIG. 3, function in the same or similar manner as previously described in regard to FIG. 1. The only difference is that the respective conduits in FIG. 3 have been labeled differently to account for the particular system embodiment depicted in FIG. 3. Furthermore, the remaining steps involved in liquefying the hydrocarbon-containing gas not addressed above in regard to FIG. 3 (conduits 310, 312, 314, 316, 318, 328, 330, 332, and 334) and the unaccounted steps in the first closed-loop mixed refrigeration cycle (conduits 336, 338, 340, 342, 344, 346, 348, 350, 352, 354, 356, 358, 360, 362, and 368) function in the same or similar manner as previously described in regard to FIG. 1.

In FIG. 4, an LNG recovery facility 10 is depicted that contains a turboexpander 94 operably connected via conduit 420 to the third cooling zone 32 of the first refrigeration system 12. As shown in FIG. 4, at least a portion of the hydrocarbon-containing feed gas stream passing through the cooling pass 34 of third cooling zone 32 can be directed via conduit 420 to the turboexpander 94, where it can be expanded into a two-phase stream. The turboexpander 94 can operate under the same or similar conditions as previously described in regard to FIG. 2. Although not depicted in FIG. 4, a suction drum may be in fluid communication between the turboexpander 94 and third cooling zone 32 in certain embodiments.

The expanded two-phase stream in conduit 422 is then directed to a separator 98 that separates the expanded stream into a liquid heavy fraction that is methane-poor (conduit 424) and an overhead vapor fraction that is methane-rich (conduit 426). The separator 98 can be the same separation vessel as described previously in regard to FIG. 2 and may function under similar operating conditions. After separation, the overhead vapor fraction in conduit 426 is then reintroduced into cooling pass 34 of third cooling zone 32 to be further cooled and condensed as described above in regard to FIG. 1.

The methane-poor bottom stream in conduit 424 can be in the form of a liquid and can contain most of the compounds having six or more carbon atoms originally found in the stream in conduit 422. For example, the methane-poor bottom stream in conduit 324 can comprise at least 70, 80, 90, 95, or 99 percent of the compounds having six or more carbon atoms originally present in the stream from conduit 422.

The methane-rich overhead vapor stream in conduit 426 can comprise a large portion of methane. For example, the methane-rich overhead vapor stream in conduit 426 can comprise at least about 10, 25, 40, or 50 and/or not more than about 99.9, 99, 95, or 85 mole percent of methane. More particularly, the methane-rich overhead vapor stream in conduit 426 can comprise in the range of about 10 to 99.9, 25 to 99, 40 to 95, or 50 to 85 mole percent of methane. Furthermore, the methane-rich overhead vapor stream in conduit 426 can comprise at least 50, 60, 70, 80, 90, 95, 99, or 99.9 percent of the methane originally present in the stream from conduit 422.

Turning again to FIG. 4, the turboexpander 94 is connected to a compressor 96 via shaft 95. The compressor 96 can be at least partially driven from work derived from the turboexpander 94. As shown in FIG. 4, the vaporized, gaseous second mixed refrigerant leaves refrigerant warming pass 42 in the cooling zone 38 via conduit 468 and is then introduced into the compressor 96, where it is compressed prior to introduction into the compressor 72. After compression, the compressed stream in conduit 470 is introduced into first compressor stage 74 and is further treated as discussed above in regard to FIG. 1. Although not depicted in FIG. 4, a suction drum may be in fluid communication between the compressor 96 and warming pass 42.

It should be noted that the first refrigeration system 12, the second refrigeration system 14, and the first closed-loop mixed refrigeration cycle (conduits 436, 438, 440, 442, 444, 446, 448, 450, 452, 454, 456, 458, 460, 462, 464, and 466) depicted in FIG. 4, which were not described above in regard to FIG. 4, function in the same or similar manner as previously described in regard to FIG. 1. The only difference is that the respective conduits in FIG. 4 have been labeled differently to account for the particular system embodiment depicted in FIG. 4. Furthermore, the remaining steps involved in liquefying the hydrocarbon-containing gas not addressed above in regard to FIG. 4 (conduits 410, 412, 414, 416, 418, 428, 430, 432, and 434) and the unaccounted steps in the second closed-loop mixed refrigeration cycle (conduits 472, 474, 476, 478, 480, 482, 484, 486, 488, and 490) function in the same or similar manner as previously described in regard to FIG. 1.

In FIG. 5, an LNG recovery facility 10 is depicted that contains a turboexpander 94 operably connected via conduit 522 to cooling zone 38 of the second refrigeration system 14. As shown in FIG. 5, at least a portion of the hydrocarbon-containing feed gas stream passing through the cooling pass 40 of cooling zone 38 can be directed via conduit 522 to the turboexpander 94, where it can be expanded into a two-phase stream. The turboexpander 94 can operate under the same or similar conditions as previously described in regard to FIG. 2. Although not depicted in FIG. 5, a suction drum may be in fluid communication between the turboexpander 94 and cooling zone 38 in certain embodiments.

The expanded two-phase stream in conduit 524 is then directed to a separator 98 that separates the expanded stream into a liquid heavy fraction that is methane-poor (conduit 526) and an overhead vapor fraction that is methane-rich (conduit 528). The separator 98 can be the same separation vessel as described previously in regard to FIG. 2 and may function under similar operating conditions.

The methane-poor bottom stream in conduit 526 can be in the form of a liquid and can contain most of the compounds having six or more carbon atoms originally found in the stream in conduit 524. For example, the methane-poor bottom stream in conduit 526 can comprise at least 70, 80, 90, 95, or 99 percent of the compounds having six or more carbon atoms originally present in the stream from conduit 524.

The methane-rich overhead vapor stream in conduit 528 can comprise a large portion of methane. For example, the methane-rich overhead vapor stream in conduit 528 can comprise at least about 10, 25, 40, or 50 and/or not more than about 99.9, 99, 95, or 85 mole percent of methane. More particularly, the methane-rich overhead vapor stream in conduit 528 can comprise in the range of about 10 to 99.9, 25 to 99, 40 to 95, or 50 to 85 mole percent of methane. Furthermore, the methane-rich overhead vapor stream in conduit 528 can comprise at least 50, 60, 70, 80, 90, 95, 99, or 99.9 percent of the methane originally present in the stream from conduit 524.

Turning again to FIG. 5, the turboexpander 94 is connected to a compressor 96 via shaft 95. The compressor 96 can be at least partially driven from work derived from the turboexpander 94. As shown in FIG. 5, the methane-rich overhead vapor stream in conduit 528 can be directed to compressor 96, which compresses the stream. The compressed stream in conduit 530 is then reintroduced into cooling pass 40 of cooling zone 38 to be further condensed and subcooled as described above in regard to FIG. 1.

It should be noted that the first refrigeration system 12, the second refrigeration system 14, the first closed-loop mixed refrigeration cycle (conduits 538, 540, 542, 544, 546, 548, 550, 552, 554, 556, 558, 560, 562, 564, 566, and 568), and the second closed-loop mixed refrigeration cycle (conduits 570, 572, 574, 576, 578, 580, 582, 584, 586, 588, and 590) depicted in FIG. 5, which were not described above in regard to FIG. 5, function in the same or similar manner as previously described in regard to FIG. 1. The only difference is that the respective conduits in FIG. 5 have been labeled differently to account for the particular system embodiment depicted in FIG. 5. Furthermore, the remaining steps involved in liquefying the hydrocarbon-containing gas not addressed above in regard to FIG. 5 (conduits 510, 512, 514, 516, 518, 520, 532, 534, and 536) function in the same or similar manner as previously described in regard to FIG. 1.

In FIG. 6, an LNG recovery facility 10 is depicted that contains a turboexpander 94 operably connected via conduit 622 to cooling zone 38 of the second refrigeration system 14. As shown in FIG. 6, at least a portion of the hydrocarbon-containing feed gas stream passing through the cooling pass 40 of cooling zone 38 can be directed via conduit 622 to the turboexpander 94, where it can be expanded into a two-phase stream. The turboexpander 94 can operate under the same or similar conditions as previously described in regard to FIG. 2. Although not depicted in FIG. 6, a suction drum may be in fluid communication between the turboexpander 94 and cooling zone 38 in certain embodiments.

The expanded two-phase stream in conduit 624 is then directed to a separator 98 that separates the expanded stream into a liquid heavy fraction that is methane-poor (conduit 626) and an overhead vapor fraction that is methane-rich (conduit 628). The separator 98 can be the same separation vessel as described previously in regard to FIG. 2 and may function under similar operating conditions. After separation, at least a portion of the overhead vapor fraction in conduit 628 is then reintroduced into cooling pass 40 of cooling zone 38 to be further condensed and subcooled as described above in regard to FIG. 1.

The methane-poor bottom stream in conduit 626 can be in the form of a liquid and can contain most of the compounds having six or more carbon atoms originally found in the stream in conduit 624. For example, the methane-poor bottom stream in conduit 626 can comprise at least 70, 80, 90, 95, or 99 percent of the compounds having six or more carbon atoms originally present in the stream from conduit 624.

The methane-rich overhead vapor stream in conduit 628 can comprise a large portion of methane. For example, the methane-rich overhead vapor stream in conduit 628 can comprise at least about 10, 25, 40, or 50 and/or not more than about 99.9, 99, 95, or 85 mole percent of methane. More particularly, the methane-rich overhead vapor stream in conduit 628 can comprise in the range of about 10 to 99.9, 25 to 99, 40 to 95, or 50 to 85 mole percent of methane. Furthermore, the methane-rich overhead vapor stream in conduit 628 can comprise at least 50, 60, 70, 80, 90, 95, 99, or 99.9 percent of the methane originally present in the stream from conduit 624.

Turning again to FIG. 6, the turboexpander 94 is connected to a compressor 96 via shaft 95. The compressor 96 can be at least partially driven from work derived from the turboexpander 94. As shown in FIG. 6, the vaporized, gaseous first mixed refrigerant leaves refrigerant warming pass 36 in the third cooling zone 32 via conduit 664 and is then introduced into the compressor 96, where it is compressed prior to introduction into the compressor 48. After compression, the compressed stream in conduit 666 is introduced into the first compressor stage 54 and is further treated as discussed above in regard to FIG. 1. Although not depicted in FIG. 6, a suction drum may be in fluid communication between the compressor 96 and warming pass 36.

It should be noted that the first refrigeration system 12, the second refrigeration system 14, and the second closed-loop mixed refrigeration cycle (conduits 670, 672, 674, 676, 678, 680, 682, 684, 686, 688, and 690) depicted in FIG. 6, which were not described above in regard to FIG. 6, function in the same or similar manner as previously described in regard to FIG. 1. The only difference is that the respective conduits in FIG. 6 have been labeled differently to account for the particular system embodiment depicted in FIG. 6. Furthermore, the remaining steps involved in liquefying the hydrocarbon-containing gas not addressed above in regard to FIG. 6 (conduits 610, 612, 614, 616, 618, 620, 630, 632, and 634) and the unaccounted steps in the first closed-loop mixed refrigeration cycle (conduits 636, 638, 640, 642, 644, 646, 648, 650, 652, 654, 656, 658, 660, 662, and 668) function in the same or similar manner as previously described in regard to FIG. 1.

In FIG. 7, an LNG recovery facility 10 is depicted that contains a turboexpander 94 operably connected via conduit 722 to cooling zone 38 of the second refrigeration system 14. As shown in FIG. 7, at least a portion of the hydrocarbon-containing feed gas stream passing through the cooling pass 40 of cooling zone 38 can be directed via conduit 722 to the turboexpander 94, where it can be expanded into a two-phase stream. The turboexpander 94 can operate under the same or similar conditions as previously described in regard to FIG. 2. Although not depicted in FIG. 7, a suction drum may be in fluid communication between the turboexpander 94 and cooling zone 38 in certain embodiments.

The expanded two-phase stream in conduit 724 is then directed to a separator 98 that separates the expanded stream into a liquid heavy fraction that is methane-poor (conduit 726) and an overhead vapor fraction that is methane-rich (conduit 728). The separator 98 can be the same separation vessel as described previously in regard to FIG. 2 and may function under similar operating conditions. After separation, at least a portion of the overhead vapor fraction in conduit 728 is then reintroduced into cooling pass 40 of cooling zone 38 to be further condensed and subcooled as described above in regard to FIG. 1.

The methane-poor bottom stream in conduit 726 can be in the form of a liquid and can contain most of the compounds having six or more carbon atoms originally found in the stream in conduit 724. For example, the methane-poor bottom stream in conduit 626 can comprise at least 70, 80, 90, 95, or 99 percent of the compounds having six or more carbon atoms originally present in the stream from conduit 724.

The methane-rich overhead vapor stream in conduit 728 can comprise a large portion of methane. For example, the methane-rich overhead vapor stream in conduit 728 can comprise at least about 10, 25, 40, or 50 and/or not more than about 99.9, 99, 95, or 85 mole percent of methane. More particularly, the methane-rich overhead vapor stream in conduit 728 can comprise in the range of about 10 to 99.9, 25 to 99, 40 to 95, or 50 to 85 mole percent of methane. Furthermore, the methane-rich overhead vapor stream in conduit 728 can comprise at least 50, 60, 70, 80, 90, 95, 99, or 99.9 percent of the methane originally present in the stream from conduit 724.

Turning again to FIG. 7, the turboexpander 94 is connected to a compressor 96 via shaft 95. The compressor 96 can be at least partially driven from work derived from the turboexpander 94. As shown in FIG. 7, the vaporized, gaseous second mixed refrigerant leaves refrigerant warming pass 42 in the cooling zone 38 via conduit 768 and is then introduced into the compressor 96, where it is compressed prior to introduction into the compressor 72. After compression, the compressed stream in conduit 770 is introduced into first compressor stage 74 and is further treated as discussed above in regard to FIG. 1. Although not depicted in FIG. 7, a suction drum may be in fluid communication between the compressor 96 and warming pass 42.

It should be noted that the first refrigeration system 12, the second refrigeration system 14, and the first closed-loop mixed refrigeration cycle (conduits 736, 738, 740, 742, 744, 746, 748, 750, 752, 754, 756, 758, 760, 762, 764, and 766) depicted in FIG. 7, which were not described above in regard to FIG. 7, function in the same or similar manner as previously described in regard to FIG. 1. The only difference is that the respective conduits in FIG. 7 have been labeled differently to account for the particular system embodiment depicted in FIG. 7. Furthermore, the remaining steps involved in liquefying the hydrocarbon-containing gas not addressed above in regard to FIG. 7 (conduits 710, 712, 714, 716, 718, 720, 730, 732, and 734) and the unaccounted steps in the second closed-loop mixed refrigeration cycle (conduits 772, 774, 776, 778, 780, 782, 784, 786, 788, and 790) function in the same or similar manner as previously described in regard to FIG. 1.

DEFINITIONS

It should be understood that the following is not intended to be an exclusive list of defined terms. Other definitions may be provided in the foregoing description, such as, for example, when accompanying the use of a defined term in context.

As used herein, the terms “a,” “an,” and “the” mean one or more.

As used herein, the term “and/or,” when used in a list of two or more items, means that any one of the listed items can be employed by itself or any combination of two or more of the listed items can be employed. For example, if a composition is described as containing components A, B, and/or C, the composition can contain A alone; B alone; C alone; A and B in combination; A and C in combination, B and C in combination; or A, B, and C in combination.

As used herein, the terms “comprising,” “comprises,” and “comprise” are open-ended transition terms used to transition from a subject recited before the term to one or more elements recited after the term, where the element or elements listed after the transition term are not necessarily the only elements that make up the subject.

As used herein, the terms “having,” “has,” and “have” have the same open-ended meaning as “comprising,” “comprises,” and “comprise” provided above.

As used herein, the terms “including,” “include,” and “included” have the same open-ended meaning as “comprising,” “comprises,” and “comprise” provided above.

As used herein, the terms “first,” “second,” “third,” and the like are used to describe various elements and such elements should not be limited by these terms. These terms are only used to distinguish one element from another and do not necessarily imply a specific order or even a specific element. For example, an element may be regarded as a “first” element in the description and a “second” element in the claims without departing from the scope of the present invention. Consistency is maintained within the description and each independent claim, but such nomenclature is not necessarily intended to be consistent therebetween.

NUMERICAL RANGES

The present description uses numerical ranges to quantify certain parameters relating to the invention. It should be understood that when numerical ranges are provided, such ranges are to be construed as providing literal support for claim limitations that only recite the lower value of the range as well as claim limitations that only recite the upper value of the range. For example, a disclosed numerical range of 10 to 100 provides literal support for a claim reciting “greater than 10” (with no upper bounds) and a claim reciting “less than 100” (with no lower bounds).

CLAIMS NOT LIMITED TO DISCLOSED EMBODIMENTS

The preferred forms of the invention described above are to be used as illustration only, and should not be used in a limiting sense to interpret the scope of the present invention. Modifications to the exemplary embodiments, set forth above, could be readily made by those skilled in the art without departing from the spirit of the present invention.

The inventors hereby state their intent to rely on the Doctrine of Equivalents to determine and assess the reasonably fair scope of the present invention as it pertains to any apparatus not materially departing from but outside the literal scope of the invention as set forth in the following claims. 

1. A process for liquefying a hydrocarbon-containing gas, the process comprising: (a) introducing a first mixed refrigerant and a feed stream comprising the hydrocarbon containing gas into a first refrigeration system; (b) cooling at least a portion of the feed stream in the first refrigeration system via indirect heat exchange with the first mixed refrigerant to form a first cooled feed stream; (c) cooling at least a portion of the first cooled feed stream in a second refrigeration system via indirect heat exchange with a second mixed refrigerant to form a second cooled feed stream; (d) expanding at least a portion of the first cooled feed stream or the second cooled feed stream in a turboexpander to form an expanded feed stream; (e) separating at least a portion of the expanded feed stream in a separator to form an overhead vapor fraction and a liquid bottom fraction; (f) cooling at least a portion of the overhead vapor fraction in the first refrigeration system or the second refrigeration system; and (g) driving a compressor with the turboexpander.
 2. The process of claim 1, further comprising expanding at least a portion of the first mixed refrigerant to form an expanded first mixed refrigerant, wherein the expanded first mixed refrigerant is used as the first mixed refrigerant during the cooling of step (b).
 3. The process of claim 2, further comprising subcooling at least a portion of the first mixed refrigerant in step (b) to form a subcooled first mixed refrigerant, wherein the subcooled first mixed refrigerant is the first mixed refrigerant subjected to expansion.
 4. The process of claim 1, further comprising expanding at least a portion of the second mixed refrigerant to form an expanded second mixed refrigerant, wherein the expanded second mixed refrigerant is used as the second mixed refrigerant during the cooling of step (c).
 5. The process of claim 4, further comprising subcooling at least a portion of the second mixed refrigerant in step (c) to form a subcooled second mixed refrigerant, wherein the subcooled second mixed refrigerant is the second mixed refrigerant subjected to expansion.
 6. The process of claim 1, wherein the first cooled feed stream is expanded during the expanding of step (d), wherein the overhead vapor fraction is cooled in the first refrigeration system.
 7. The process of claim 1, wherein the second cooled feed stream is expanded during the expanding of step (d), wherein the overhead vapor fraction is cooled in the second refrigeration system.
 8. The process of claim 1, wherein the compressor compresses at least a portion of the first mixed refrigerant.
 9. The process of claim 1, wherein the compressor compresses at least a portion of the second mixed refrigerant.
 10. The process of claim 1, wherein the compressor compresses at least a portion of the overhead vapor fraction prior to the cooling of step (f).
 11. A process for liquefying a hydrocarbon-containing gas, the process comprising: (a) introducing a first mixed refrigerant and a feed stream comprising the hydrocarbon-containing gas into a first refrigeration system; (b) cooling at least a portion of the feed stream in the first refrigeration system via indirect heat exchange with the first mixed refrigerant to form a first cooled feed stream; (c) cooling at least a portion of the first cooled feed stream in a second refrigeration system via indirect heat exchange with a second mixed refrigerant to form a second cooled feed stream; (d) separating at least a portion of the second cooled feed stream in a separator to form an overhead vapor fraction and a liquid bottom fraction; and (e) cooling at least a portion of the overhead vapor fraction in the first refrigeration system or the second refrigeration system.
 12. The process of claim 11, further comprising expanding at least a portion of the first mixed refrigerant to form an expanded first mixed refrigerant, wherein the expanded first mixed refrigerant is used as the first mixed refrigerant during the cooling of step (b).
 13. The process of claim 12, further comprising subcooling at least a portion of the first mixed refrigerant in step (b) to form a subcooled first mixed refrigerant, wherein the subcooled first mixed refrigerant is the first mixed refrigerant subjected to expansion.
 14. The process of claim 11, further comprising expanding at least a portion of the second mixed refrigerant to form an expanded second mixed refrigerant, wherein the expanded second mixed refrigerant is used as the second mixed refrigerant during the cooling of step (c).
 15. The process of claim 14, further comprising subcooling at least a portion of the second mixed refrigerant in step (c) to form a subcooled second mixed refrigerant, wherein the subcooled second mixed refrigerant is the second mixed refrigerant subjected to expansion.
 16. The process of claim 11, further comprising expanding at least a portion of the second cooled feed stream in a turboexpander to form an expanded feed stream, wherein the expanded feed stream is the second cooled feed stream in the separating of (d).
 17. The process of claim 16, further comprising a compressor at least partially driven by the turboexpander, wherein the compressor at least partially compresses the first mixed refrigerant, the second mixed refrigerant, or the overhead vapor fraction.
 18. The process of claim 17, wherein the compressor at least partially compresses the first mixed refrigerant.
 19. The process of claim 17, wherein the compressor at least partially compresses the second mixed refrigerant.
 20. The process of claim 17, wherein the compressor at least partially compresses the overhead vapor fraction.
 21. The process of claim 11, cooling at least a portion of the overhead vapor fraction in the second refrigeration system.
 22. A system for liquefying a hydrocarbon-containing gas, the system comprising: (a) a first refrigeration system comprising a first cooling zone disposed therein, wherein the first cooling zone is configured to cool a feed stream comprising the hydrocarbon-containing gas via indirect heat exchange with a first mixed refrigerant to form a first cooled feed stream; (b) a first closed-loop mixed refrigeration cycle at least partially disposed within the first refrigeration system, wherein the first closed-loop mixed refrigeration cycle comprises the first mixed refrigerant; (c) a second refrigeration system in fluid communication with the first refrigeration system, wherein the second refrigeration system comprises a second cooling zone disposed therein, wherein the second cooling zone is configured to cool the first cooled feed stream via indirect heat exchange with a second mixed refrigerant to form a second cooled feed stream; (d) a second closed-loop mixed refrigeration cycle at least partially disposed within the second refrigeration system, wherein the second closed-loop mixed refrigeration cycle comprises the second mixed refrigerant; (e) a turboexpander in fluid communication with the first refrigeration system or second refrigeration system, wherein the turboexpander is configured to expand the first cooled feed stream or the second cooled feed stream into an expanded stream; (f) a separator in fluid communication with the turboexpander, wherein the separator is configured to separate the expanded stream into an overhead vapor fraction and a liquid bottom fraction; (g) a conduit for returning at least a portion of the overhead vapor fraction to the first refrigeration system or second refrigeration system; and (h) a compressor at least partially driven from work derived from the turboexpander, wherein the compressor is configured to at least partially compress the first mixed refrigerant, the second mixed refrigerant, or the overhead vapor fraction.
 23. The system of claim 22, wherein the turboexpander is in fluid communication with the first refrigeration system and the conduit returns at least a portion of the overhead vapor fraction to the first refrigeration system.
 24. The system of claim 22, wherein the turboexpander is in fluid communication with the second refrigeration system and the conduit returns at least a portion of the overhead vapor fraction to the second refrigeration system. 